Purpose: Based on the assumption that the economic weight of endometriosis is underestimated, a cost-of-illness study was performed. The aim was to determine the costs in order to estimate the economic burden of this disease on society as a whole. Materials and Methods: Data was collected using a questionnaire that included sociodemographic data, quality-of-life (SF-12), use of healthcare facilities, and job situation. The study included two study populations: (a) members of the German Endometriosis Association; (b) patients from inpatient rehabilitation centres. Results: The average cost per individual amounted to 5622 Euros, of which the indirect costs comprised 62% of the total costs. Costs resulting from patients' inability to work and hospitalization constituted up to 49 and 31% of the total costs, respectively. An extrapolation of these figures for the whole of Germany yielded the sum of 1.96 billion Euros for the year 2003. Conclusion: With costs of 1.96 billion Euros endometriosis is a condition that should not be ignored. In younger populations (average age 36.7 years), long periods where patients are unable to work increases the risk of job losses. Therefore, intensive medical care should aim at patients becoming symptom-free.